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doi: 10.3823/269
Plasmid mediated extended spectrum
beta-lactamase producing strains of
enterobacteriaceae isolated from diabetic foot
infections in Egypt
1 Department of Microbiology, Faculty of Pharmacy, Misr International University (MIU), Cairo, Egypt.
2 Department of Microbiology and Immunology, Faculty of Pharmacy, Ain Shams University, Organization of African Unity St., POB: 11566, Abbassia, Cairo, Egypt.
Correspondence:
Kamel, Noha. A 1, Aboshanab, Khaled M.2, Abouelwafa, Mohammad M.2, El-tayeb, Wafaa N.1
This article is available from: www.acmicrob.com
Abstract
Background: Extended spectrum beta-lactamases (ESBLs) are heterogeneous group of plasmid mediated β-lactamases enzymes that confer resistant to oxyimino cephalosporins, monobactam (aztreonam) and usually show co-resistance to other classes of antibiotics. The present was done to identify and characterize the most common plasmid-mediated ESBL genes associated with diabetic foot infections in Egypt.
Methods and findings: A total of 135 Gram negative bacterial isolates were re-covered from 91 diabetic foot ulcers specimens of patients attending governmental hospitals and private clinics in Cairo, Egypt. The antibiogram analysis revealed a remarkable high resistance pattern towards different classes of the tested antimi-crobial agents. Based on CLSI, a total of 114 isolates out of 135 were considered potential ESBLs producer by using disc diffusion and broth microdilution screening assays followed by double disc synergy test (DDST). 58 out of 114 isolates were ESBLs producers and almost 14% (8 out of 58), were plasmid-mediated as deter-mined by plasmid extraction and transformation experiments. The majority of the tested plasmids (6 out of 8) carried 2 or more genes on the same plasmid. The most common combination was blaCTX-M and blaTEM (n=3/8; 37.5%), followed by blaSHV and blaCTX-M(n=2/8; 25%) and blaCTX-M+ blaTEM+ blaSHV (n=1/8;12.5%). One E.coli isolate harbored a plasmid (pECDF16) coding for the three ESBLs genes. The final nucleotide sequences of blaTEM1 and blaSHV-8 were submitted to the GenBank database under accessions coder JX976326, and JX976327, respectively.
Conclusion: High prevalence of plasmid-mediated ESBLs was detected among DFIs in Egypt. Therefore, new guidelines should be undertaken in Egypt to limit or prevent the misuse and abuse of antimicrobial agents.
Key words: ESBLs, plasmid-mediated ESBLs, Diabetic foot infections, Enterobac-teriaceae
Introduction
By year 2030, Egypt will be from the top countries that suf-fers from Diabetes mellitus [1]. Being diabetic, places patient at a high burden to develop diabetes chronic complications. Diabetic foot ulcers are considered to be one of the most common complications of diabetes, that are usually vulner-
able to infections that spreads rapidly, leading to devastating tissue destruction and increases risk of leg amputation [2]. Most diabetic foot infections (DFI) are polymicrobial (where two or more bacteria are recovered) from the same specimen. In addition to Gram positive staphylococci, Gram negative rods member of Enterobacteriaceae and Pseudomonas ae-ruginosa may be recovered [3]. One of the major concern is
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the increasing incidence of multidrug-resistant Gram negative organisms, particularly extended spectrum beta lactamases producers (ESBLs) among DFI [4].
ESBLs are Class A β-lactamases that have the ability to hydro-lyze oxyimino cephalosporins and monobactams. However, these enzymes cannot hydrolyze cephamycins or carbapen-ems [5] and they are in vitro inhibited by clavulanate [6]. The majority of the ESBLs are plasmid mediated (mega plasmids) that can has resistant determinants to quinolones and amino-glycosides in addition to, β-lactam hence limiting therapeutic options [7, 8]. Moreover, being plasmid mediated will facili-tate the propagation of these determinants among different bacterial species via horizontal transfer.
The vast majority of the clinically important ESBLs belong mainly to TEM (called after Greek girl “Temoniera”), SHV (refers to sulfhydryl variable) and CTX (called after conferred resistance to cefotaxime) genotypes [9]. These ESBLs have evolved as a result of substitutions in key amino acids of parent TEM-1/2, SHV-1 enzymes [6] and incorporation of pre-existing ESBL genes on chromosome of Kluyvera spp. onto mobile plasmid, respectively [10]. Those point mutations within ESBLs will lead to huge diversity within ESBL genotype. Subsequently, molecular characterization of all suspected Gram negative ESBL producers (phenotypically detected) is of immense important to detect the spread and to identify the exact variant within resistant genes recovered from DFIs. Therefore, this study was conducted to study prevalence of plasmid-mediated ESBLs among DFI in Egypt and determine correlation between phenotypic and genotypic data of anti-biotic resistance among relevant pathogens.
Methods
Microorganisms, and phenotypic detection of ESBLs
A total of 206 aerobic/facultative anaerobes clinical bac-terial isolates were recovered from 91 diabetic foot ulcers (DFUs). The bacterial isolates were identified via conventional methods (direct film, macroscopical characters and standard biochemical tests). Gram negative isolates were chosen to further screening for potential ESBLs producers using disc diffusion and micro broth dilution method [11, 12]. For more confirmations of ESBLs detection, the phenotypic double disc synergy test (DDST) was carried out on potential ESBLs pro-ducer [13].
Genotypic detection of plasmid-mediated ESBLs
For the detection of plasmid mediated ESBLs among our iso-lates, the phenotypically confirmed ESBLs producer by DDST, were subjected to plasmid extraction by alkaline lysis as de-scribed by Birnboim and Doly, 1979 [14]. In a trial to prove the association of these plasmids with ESBLs, genetic transfer of the extracted plasmids via transformation was carried out using competent E. coli DH5α and E. coli JM109 (Novagen, Darmstadt, Germany). These competent cells were prepared and transformed according to the modified Hanahan method [15] and Sambrook and Russell [16]. PCR technique was used to detectand amplify the most common ESBLs genes via us-ing universal primers for blaTEM [17], blaSHV [17], blaCTX-M [18] and plasmid DNA as templates. PCR amplification program was computerized using pDRAW32 (http://www.acaclone.com).
DNA sequencing of PCR products
Prior to sending PCR products to sequencing, a PCR cleanup step was performed using GeneJET Purification Kit. The pu-rified PCR products were sent to Sigma-Scientific Co. Giza, Egypt for DNA sequencing using ABI 3730xl DNA Sequence.
Computer programs used for sequence analysis
The obtained sequences files (both forward and reverse) were analyzed using a set of programs each with certain func-tion. Staden package [19] (http://staden.sourceforge.net/) was used for nucleotide sequence assembly and formation of long contigs; FramePlot [20] (http://www.nih.go.jp/~jun/cgi-bin/frameplot.pl) was used to detect open reading frames on final contigs; Clustal W [21] (http://www2.ebi.ac.uk/clust-alw) was used for amino acid alignment. Finally DNA search in the GenBank database was carried out using BLAST (Basal Local Alignment Research tool; http://www.ncbi.nlm.nih.gov/BLAST).
Results
Prevalence of the Gram negative bacterial species recovered from DFI specimens
A total of 135 Gram negative isolates representing 65.5% were recovered from 91 DFI specimens. Proteus spp. espe-cially Proteus mirabilis were among the most common recov-ered Gram negative isolates (n=44/135; 32.6%) followed by
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E. coli (n=24/135; 17.8%), followed by Pseudomonas spp. (n= 19/135; 14%) followed by Klebsiella spp. (n= 17/135; 12.6%) while other spp. such as Citrobacter spp., Morganella spp., Providencia spp. and Serratia spp. have played a minor role in bacteriology of DFIs.
Detection of ESBLs among the recovered Gram negative isolates
The overall antibiotic resistance pattern of the tested 135 isolates against various classes of antimicrobial agents by disc diffusion is summarized in Table 1. The results revealed that out of the 9 tested agents, the resistance pattern was equal to or exceeds 50% for 7 antimicrobial agents and only 10.3% of the tested isolates were resistant to imipenem indicating probability of ESBLs recovery from our isolates.
Potential ESBLs producing isolates as determined by disc dif-fusion and MIC by broth microdilution methods is summa-rized in Table 2. The results revealed that a total of 114 out of 135 were considered potential ESBL producers by disc diffu-sion (diameter of zone of inhibition was less than or equal to 25mm for ceftriaxone and/or diameter of zone of inhibition of cefotaxime and aztreonam was less than or equal to 27mm).
The results also revealed that 106 out of 135 were consid-ered potential ESBL producer by showing MIC value greater than or equals to 2μg/ml for ceftriaxone. Subsequently, all the potential ESBL producers (114) were subjected to DDST and the results revealed that 58 isolates showed clavulanic acid synergy with at least one of the tested substrates (aztreonam, cefotaxime, ceftriaxone). The highest ESBL production was detected in Proteus mirabilis. (n= 26/33; 78.7%), followed by Klebsiella spp. (n=11/15; 73.3%) and finally E. coli (n=13/20; 65%).
Table 1. Overall antibiotic resistance pattern of Gram negative bacterial isolates by disc diffusion method.
Antimicrobial class Tested antimicrobial agents No. of resistant isolates Percentage (%)
Β-lactam antibiotic
Ampicillin 135 100
Ceftriaxone 56 41.4
Cefotaxime 71 52.6
Cefepime 75 55.5
Aztreonam 74 54.8
Imipenem 14 10.3
Quinolones Ciprofloxacin 81 60
Aminoglycosides Gentamicin 75 55.5
Tetracycline Tetracycline 106 78.5
Total number of tested isolates was 135.
Table 2. Potential ESBLs producing isolates as determined by disc diffusion(a) and MIC by broth microdilution(b) methods.
Number and % of potential ESBLs producing isolates as determined by
Disc diffusion(a) MIC broth microdilution(b)
Isolate species Number % Isolate species Number %
E. coli 20 83.3 E. coli 17 70.8
Klebsiella spp. 15 88.2 Klebsiella spp. 12 70.5
Proteus spp. 38 77.5 Proteus spp. 36 73.4
Pseudomonas spp. 19 100 Pseudomonas spp. 19 100
Others* 22 84.6 Others* 22 84.6
(a) Against ceftriaxone, cefotaxime and aztreonam. Total no. of potential producing isolates by disk diffusion was 114; (b) Against ceftriaxone. Total no. of potential producing isolates by broth dilution was 106. *others: Citrobacter spp., Enterobacter spp., Providencia spp. Serratia spp. and Morganella spp. % was calculated from total number of tested isolate species.
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TEM-Ng MSIQHFRVALIPFFAAFCLPVFAHPETLVKVKDAEDQLGARVGYIELDLNSGKILESFRP 60Bla-EC MSIQHFRVALIPFFSAFCLPVFAHPETLVKVKDAEDQLGARVGYIELDLNSGKILESFRP 60ARP-EC MSIQHFRVALIPFFAAFCLPVFAHPETLVKVKDAEDQLGARVGYIELDLNSGKILESFRP 60TEM-128Ab MSIQHFRVALIPFFAAFCLPVFAHPETLVKVKDAEDQLGARVGYIELDLNSGKILESFRP 60TEM-1EC MSIQHFRVALIPFFAAFCLPVFAHPETLVKVKDAEDQLGARVGYIELDLNSGKILESFRP 60TEM-84EC MSIQHFRVALIPFFAAFCLPVFAHPETLVKVKDAEDQLGARVGYIELDLNSGKILESFRP 60TEM-104Kp MSIQHFRVALIPFFAAFCLPVFAHPETLVKVKDAEDQLGARVGYIELDLNSGKILESFRP 60TEM-query MSISHFRVALIPFFAAFCLPVFAHPETLVKVKDAEDQLGARVGYIELDLNSGKILESFRP 60 ***.**********:*********************************************
TEM-Ng EERFPMMSTFKVLLCGAVLSRVDAGQEQLGRRIHYSQNDLVEYSPVTEKHLTDGMTVREL 120Bla-EC EERFPMMSTFKVLLCGAVLSRVDAGQEQLGRRIHYSQNDLVEYSPVTEKHLTDGMTVREL 120ARP-EC EERFPMMSTFKVLLCGAVLSRIDAGQEQLGRRIHYSQNDLVEYSPVTEKHLTDGMTVREL 120TEM-128Ab EERFPMMSTFKVLLCGAVLSRVDAGQEQLGRRIHYSQNDLVEYSPVTEKHLTDGMTVREL 120TEM-1EC EERFPMMSTFKVLLCGAVLSRVDAGQEQLGRRIHYSQNDLVEYSPVTEKHLTDGMTVREL 120TEM-84EC EERFPMMSTFKVLLCGAVLSRVDAGQEQLGRRIHYSQNDLVEYSPVTEKHLTDGMTVREL 120TEM-104Kp EERFPMMSTFKVLLCGAVLSRVDAGQEQLGRRIHYSQNDLVEYSPVTEKHLTDGMTVREL 120TEM-query EERFPMMSTFKVLLCGAVLSRVDAGQEQLGRRIHYSQNDLVEYSPVTEKHLTDGMTVREL 120 *********************:**************************************
TEM-Ng CSAAITMSDNTAANLLLTTIGGPKELTAFLHNMGDHVTRLDRWEPELNEAIPNDERDTTM 180Bla-EC CSAAITMSDNTAANLLLTTIGGPKELTAFLHNMGDHVTRLDRWEPELNEAIPNDERDTTM 180ARP-EC CSAAITMSDNTAANLLLTTIGGPKELTAFLHNMGDHVTRLDRWEPELNEAIPNDERDTTM 180TEM-128Ab CSAAITMSDNTAANLLLTTIGGPKELTAFLHNMGDHVTRLDRWEPELNEAIPNDERDTTM 180TEM-1EC CSAAITMSDNTAANLLLTTIGGPKELTAFLHNMGDHVTRLDRWEPELNEAIPNDERDTTM 180TEM-84EC CSAAITMSDNTAANLLLTTIGGPKELTAFLHNMGDHVTRLDRWEPELNEAIPNDERDTTM 180TEM-104Kp CSAAITMSDNTAANLLLTTIGGPKELTAFLHNMGDHVTRLDRWEPELNEAIPNDERDTTM 180TEM-query CSAAITMSDNTAANLLLTTIGGPKELTAFLHNMGDHVTRLDRWEPELNEAIPNDERDTTM 180 ************************************************************
TEM-Ng PAAMATTLRKLLTGELLTLASRQQLIDWMEADKVAGPLLRSALPAGWFIADKSGAGERGS 240Bla-EC PAAMATTLRKLLTGELLTLASRQQLIDWMEADKVAGPLLRSALPAGWFIADKSGAGERGS 240ARP-EC PAAMATTLRKLLTGELLTLASRQQLIDWMEADKVAGPLLRSALPAGWFIADKSGAGERGS 240TEM-128Ab PAAMATTLRKLLTGELLTLASRQQLIDWMEADKVAGPLLRSALPAGWFIADKSGAGERGS 240TEM-1EC PAAMATTLRKLLTGELLTLASRQQLIDWMEADKVAGPLLRSALPAGWFIADKSGAGERGS 240TEM-84EC PAAMATTLRKLLTGELLTLASRQQLIDWMEADKVAGPLLRSALPAGWFIADKSGAGERGS 240TEM-104Kp PAAMATTLRKLLTGELLTLASRQQLIDWMEADKVAGPLLRSALPAGWFIADKSGAGERGS 240TEM-query PAAMATTLRKLLTGELLTLASRQQLIDWMEADKVAGPLLRSALPAGWFIADKSGAGERGS 240 ************************************************************
Plasmid extraction and transformation experiments
All phenotypically confirmed ESBLs producer by DDST (58 isolates) were screened for plasmids acquisition and only 8 isolates showed plasmid bands. Subsequently, transformation assay were conducted on the 8 isolates and the results re-vealed that plasmids extracted from E. coli, Proteus mirabilis and Klebsiella spp. were successfully transformed into E. coli DH5α, while in case of E. coli JM109 only 2 plasmids (ex-tracted from two Proteus mirabilis isolates 26-1 and 29-1) could not be transformed.
Molecular characterization of plasmid-mediated ESBLs genes
The plasmids extracted from 3 E. coli isolates (28-1, 78-1 and 79-1), 4 Proteus mirabils isolates (26-1, 74-1, 9-1 and 72-1) and 1 Klebsiella pneumonia isolate (74-2) were used as
templates for amplification of blaTEM, blaSHV and blaCTX-M genes. The results revealed the apparent existence of blaTEM, blaSHV and blaCTXM in extracted plasmids of 4 (26-1, 72-1, 78-1, 79-1); 3 (74-2, 9-1 and 79-1) and 8 (28-1, 78-1, 79-1, 26-1, 74-1, 9-1, 72-1, 74-2) of the tested isolates, respectively.For further verification of the type of ESBLs detected by PCR, DNA sequence analysis of the PCR products obtained upon using the plasmid pECDF16 extracted from the E. coli isolate (79-1) as a template was done. Sequence analysis of the re-spective PCR products revealed the presence of the three ESBL genes (blaTEM, blaSHV and blaCTX-M) on this plasmid. The final nucleotide sequences of blaTEM, blaSHV located on pECDF16 plasmid were submitted to the nucleotide GenBank database under accession codes, JX976326 and JX976327 (http://www.ncbi.nlm.nih.gov/nuccore/JX976326) and JX976327 (http://www.ncbi.nlm.nih.gov/nuccore/JX976327), respectively. The results of multiple sequence alignments of blaTEM, blaSHV and blaCTX-M with their homologous proteins using ClustalW software are depicted in Figures 1, 2 and 3.
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TEM-Ng RGIIAALGPDGKPSRIVVIYTTGSQATMDERNRQIAEIGASLIKHW 286Bla-EC RGIIAALGPDGKPSRIVVIYTTGSQATMDERNRQIAEIGASLIKHW 286ARP-EC RGIIAALGPDGKPSRIVVIYTTGSQATMDERNRQIAEIGASLIKHW 286TEM-128Ab RGIIAALGPDGKPSRIVVIYTTGSQATMDERNRQIAEIGTSLIKHW 286TEM-1EC RGIIAALGPDGKPSRIVVIYTTGSQATMDERIRQIAEIGASLIKHW 286TEM-84EC RGIIAALGPDGKPSRIVVIYTTGSQATMDERDRQIAEIGASLIKHW 286TEM-104Kp RGIIAALGPDGKPSRIVVIYTTGSQATMDERNRQIVEIGASLIKHW 286TEM-query RGIIAALGPDGKPSRIVVIYTTGSQATMDERMSQIVDMGGSLIKHW 286 ******************************* **.::* ******
Figure 1. Multiple alignment of amino acid sequence of TEM-query Beta-lactamase of Escherichia coli isolate/pECDF16 (AC=JX976326) against its homologous in the Gen Bank database: TEM-Ng = beta-lactamase, Neisseria gonorrhoeae, AC= NP_052173; Bla-EC= beta-lactamase, Escherichia coli O83:H1 str. NRG 857C; AC= YP_006162231; ARP-EC = ampicillin resistance protein, Escherichia coli, AC= YP_006952162; TEM-128Ab = beta-lactamase TEM-128, Acinetobacter baumannii, AC=AAQ57123; TEM-1EC =TEM-1 beta lactamases Escherichia coli, AC=ACJ43258; TEM-84EC= beta-lactamase TEM-84, Escherichia coli, AC=AAL29436; and TEM-104Kp =1 beta-lactamase TEM-104, Klebsiella pneumonia, AC= ACJ43258. The numbers indicate positions within the corresponding proteins. AC = Gen Bank accession number.
SHV-Yp MRYIRLCIISLLATLPLAVHASPQPLEQIKLSESQLSGRVGMIEMDLASGRTLTAWRADE 60SHV-95Cf MRYIRLCIISLLATLPLAVHASPQPLEQIKLSESQLSGRVGMIEMDLASGRTLTAWRADE 60SHV-48kp MRYIRLCIISLLATLPLAVHASPQPLEQIKLSESQLSGRVGMIEMDLASGRTLTAWRADE 60SHV-EC MRYIRLCIISLLATLPLAVHASPQPLEQIKLSESQLSGRVGMIEMDLASGRTLTAWRADE 60SHV-148KL MRYIRLCIISLLATLPLAVHASPQPLEQIKLSESQLSGRVGMIEMDLASGRTLTAWRADE 60SHV-8 query MAYIRLCIISLLATLPLAVHASPQPLEQIKLSESQLSGRVGMIEMDLASGRTLTAWRADE 60 * **********************************************************
SHV-Yp RFPMMSTFKVVLCGAVLARVDAGDEQLERKIHYRQQDLVDYSPVSEKHLADGMTVGELCA 120SHV-95Cf RFPMMSTFKVVLCGAVLARVDAGDEQLERKIHYRQQDLVDYSPVSEKHLADGMTVGELCA 120SHV-48kp RFPMMSTFKVVLCGAVLARVDAGDEQLERKIHYRQQDLVDYSPVSEKHLADGMTIGELCA 120SHV-EC RFPMMSTFKVVLCGAVLARVDAGDEQLERKIHYRQQDLVDYSPVSEKHLADGMTVGELCA 120SHV-148KL RFPMMSTFKVVLCGAVLARVDAGDEQLERKIHYRQQDLVDYSPVSEKHLADGMTVGELCA 120SHV-8query RFPMMSTFKVVLCGAVLARVDAGDEQLERKIHYRQQDLVDYSSVSEKHLAGGMTVGELCA 120 ******************************************.*******.***:*****
SHV-Yp AAITMSDNSAANLLLATVGGPAGLTAFLRQIGDNVTRLDRWETELNEALPGDARDTTTPA 180SHV-95Cf AAITMSDNSAANLLLATVGGPAGLTAFLRQIGDNVTRLDRWETELNEALPGDARDTTTPA 180SHV-48kp AAITMSDNSAANLLLATVGGPAGLTAFLRQIGDNVTRLDRWETELNEALPGDARDTTTPA 180SHV-EC AAITMSDNSAANLLLATVGGPAGLTAFLRQIGDNVTRLDRWETERNEALPGDARDTTTPA 180SHV-148KL AAITMSDNSAANLLLATVGGPAGLTAFLRQIGDNVTRLDRWETELNEALPGDARDTTTPA 180SHV-8query AAMTMSDNRAANLLLATVGGPAGLIAFLSQIGDNVTRLDRWETEVNEALPGDARDTTTPA 180 **:***** *************** *** *************** ***************
SHV-Yp SMAATLRKLLTSQRLSARSQRQLLQWMVDDRVAGPLIRSVLPAGWFIADKTGAGERGARG 240SHV-95Cf SMAATLRKLLTSQRLSARLQRQLLQWMVDDRVAGPLIRSVLPAGWFIADKTGAGERGARG 240SHV-48kp SMAATLRKLLTSQRLSARSQRQLLQWMVDDRVAGPLIRSVLPAGWFIADKTGAGERGARG 240SHV-EC SMAATLRKLLTSQRLSARSQRQLLQWMVDDRVAGPLIRSVLPAGWFIADKTGAGERGARG 240SHV-148KL SMAATLRKLLTSQRLSARSQRQLLQWMVDDRVAGPLIRSVLPAGWFIADKTGAGERGARG 240SHV-8 query SMAATLRKLLTSQRLSARSQRQLLQWMVDDRVAGPLIRSVLPAGWFIADKTGAGERGARG 240 ****************** *****************************************
SHV-Yp IVALLGPNNKAERIVVIYLRDTPASMAERNQQIAGIGAALIEHWQR 286SHV-95Cf IVALLGPNNKAERIVVIYLRDTPASMAERNQQIAGIGAALIEHWQR 286SHV-48kp IVALLGPNNKAERIVVIYLRDTPASMAERNQQIAGIGAALIEHWQR 286SHV-EC IVALLGPNNKAERIVVIYLRDTPASMAERNQQIAGIGAALIEHWQR 286SHV-148KL IVALLGPNNKAERIVVIYLRDTPASMAERNQQIAGIGAALIEHWQQ 286SHV-8 query IVALLGPNNKAERIVVIYLRDTPASMAERNQQIAGIGAALIEHWQT 286 *********************************************
Figure 2. Multiple alignment of amino acid sequence of SHV-8 query beta-lactamase of Escherichia coli isolate/pECDF16 (AC=JX976327) against its homologous in the GenBank database: SHV-Yp = SHV of Yersinia pestis biovar orientalis str. IP275, AC = YP_001102238; SHV-95Cf = SHV-95 of Citrobacter freundii, AC = ABN49113; SHV-48kp = SHV-48 of Klebsiella pneumoniae, AC = AAP03063; SHV-EC = SHV of extended-spectrum beta-lactamase of Escherichia coli, AC = AAO66446; SHV-148KL=SHV-148 beta-lactamase of Klebsiella pneumoniae, AC = AFQ23954. The numbers indicate positions within the corresponding proteins. AC = GenBank accession number.
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EC-CTX-M15 ILYRADERFAMCSTSKVMAAAAVLKKSESEPNLLNQRVEIKKSDLVNYNPIAEKHVNGTM 120SS-CTX-M3 ILYRADERFAMCSTSKVMAAAAVLKKSESEPNLLNQRVEIKKSDLVNYNPIAEKHVNGTM 106KP-CTX-M3 ILYRADERFAMCSTSKVMAAAAVLKKSESEPNLLNQRVEIKKSDLVNYNPIAEKHVNGTM 104SB-CTX-M3 ILYRADERFAMCSTSKVMAAAAVLKKSESEPNLLNQRVEIKKSDLVNYNPIAEKHVNGTM 97CTX-M3 query ---ILYRADERFAVCSTSKVMAAAAVLKKSESEPNLLNQRVEIKKSDLVNYNPIAEKHVNGTM 53EnC-CTX-M ILYRADERFAMCSTSKVMAAAAVLKKSESEPNLLNQRVEIKKSDLVNYNPIAEKHVNGTM 91 **********:*************************************************
EC-CTX-M15 SLAELSAAALQYSDNVAMNKLIAHVGGPASVTAFARQLGDETFRLDRTEPTLNTAIPGDP 180SS-CTX-M3 SLAELSAAALQYSDNVAMNKLIAHVGGPASVTAFARQLGDETFRLDRTEPTLNTAIPGDP 166KP-CTX-M3 SLAELSAAALQYSDNVAMNKLIAHVGGPASVTAFARQLGDETFRLDRTEPTLNTAIPGDP 164SB-CTX-M3 SLAELSAAALQYSDNVAMNKLIAHVGGPASVTAFARQLGDETFRLDRTEPTLNTAIPGDP 157CTX-M-3 query SLAELSAAALQYSDNVAMNKLIAHVGGPASVTAFARQLGDETFRLDRTEPTLNTAIPGDP 113EnC-CTX-M SLAELSAAALQYSDNVAMNKLIAHVGGPASVTAFARQLGDETFRLDRTEPTLNTAIPGDP 151 ************************************************************
EC-CTX-M15 RDTTSPRAMAQTLRNLTLGKALGDSQRAQLVTWMKGNTTGAASIQA-------------- 226SS-CTX-M3 RDTTSPRAMAQTLRNLTLGKALGDSQRAQLVTWMKGNTTGAASIQA-------------- 212KP-CTX-M3 RDTTSPRAMAQTLRNLTLGKALGDSQRAQLVTWMKGNTTGAASIQAGLPA---------- 214SB-CTX-M3 RDTTSPRAMAQTLRNLTLGKALGDSQRAQLVTWMKGNTTGAASIQAGLPAS--------- 208CTX-M-3 query RDTTSPRAMAQTLRNLTLGKALGDSQRAQLVTWMKGNTT--------------------- 152EnC-CTX-M RDTTSPRAMAQTLRNLTLGKALGDSQRAQLVTWMKGNTTGAASIQAGLPASWVVGDKTGS 211 ***************************************
Figure 3. Partial multiple alignment of amino acid sequence of CTX-3 query beta-lactamase of Escherichia coli isolate/pECDF16 against its homologous in the GenBank database: EC-CTX-M15 = beta-lactamase CTX-M-15, Escherichia coli, AC = ACU44517; SS-CTX-M3 = extended spectrum beta-lactamase CTX-M3, Shigella sonnei, AC = ADY02591.1; KP-CTX-M3 = CTX-M-3 beta-lactamase, Klebsiella pneumoniae, AC = AAY87935; SB-CTX-M3 = extended-spectrum beta-lactamase CTX-M-3, Shigella boydii, AC = ABK60211; EnC-CTX-M = beta-lactamase, Enterobacter cloacae, AC = ABF29659.1. The numbers indicate positions within the corresponding proteins. AC = GenBank accession number.
Discussion
The present report is an extensive study regarding the phe-notypic detection and molecular characterization of the most common plasmid mediated ESBLs genes recovered from Gram negative isolates causing DFIs in Egypt.
It is worth noting that the prevalence of members of Entero-bacteriaceae as well as Pseudomonas spp. among the recov-ered Gram negative isolates (65.5%), have raised our fear that these pyogenic bacterial infections could be ESBLs producers. Moreover, there are multiple factors that enhance recovery of these resistant isolates, among them are overuse and misuse of antibiotic, prolonged hospital stay, being diabetic with de-crease immune response and peripheral vascular diseases that limits penetration of antibiotics and hence allowing selective survival of resistant pathogens [22, 23].
With regards to CLSI, initial screening for ESBLs was per-formed by disc diffusion and broth microdilution. As shown in Table 2, a total of 114 out of 135 representing 84.4% were potential ESBL producer by disc diffusion while, a total of 106 out of 135 representing 78.5% showed MIC ≥2μg/ml for ceftriaxone. This discrepancy in results was attributed to the usage of more than one substrate such as cefotaxime,
ceftriaxone and aztreonam in the first method, while in the latter case we have tested only ceftriaxone. In addition to initial screening tests, we further confirmed ESBL producers by DDST. The results revealed that 58 out of 114 tested iso-lates (50.8%) showed synergy with at least one of the tested substrates. Moreover, the results of the current study have drawn our attention, that besides E. coli [7, 22, 24] and Kleb-siella spp.[7, 24], Proteus spp. especially Proteus mirabilisare important ESBLs producer in DFIs.
In the present study we planned to detect the prevalence of plasmid mediated ESBL producing bacteria as there is scarcity of data in our country. Almost 14% of tested isolates showed plasmid bands upon running on 0.8% agarose gel. This find-ing was compared with Motta et al., who detected a relative-ly lower percentage (6%) among Brazilians [25]. Moreover, to further confirm if these antimicrobial genes are located on plasmid or not, transformation experiments were performed. The eight tested plasmids were efficaciously transformed in E. coli DH5α, however only two plasmids of Proteus mirabilis were unsuccessfully transformed in E. coli JM109 and this could be attributed to their large size and/or difference in genotype of E. coli JM109 from that of E. coli DH5α which is relaxed mutant (relA1) characterized by production of high copy number of plasmids and hence more easily transformed.
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In addition to the phenotypic screening tests for ESBLs detec-tion, genotypic tests were done to confirm ESBL genes. PCR was used to amplify the 8 plasmid mediated ESBLs genes (blaSHV, blaTEM, blaCTX-M). The results revealed that blaCTX-
M was the most common gene (100%), followed by blaTEM (50%) and finally blaSHV (37.5%). By surveying the literature, we recorded the increased prevalence of blaCTX-M among ESBLs producer in Greece (87%) [26], Egypt (89.2%) [27] and Norway (90%) [28]. The wide spread appearance of this type of ESBLs genes could be attributed to either diversity of mo-lecular platforms associated with it as not only plasmids but, also location of blaCTX-M near or within transposons [29]. Moreover, the selective pressure exerted mainly by ceftriax-one and/or cefotaxime could be a reason behind wide spread of this type of genes [30, 31].
For further molecular characterization of variants within ESBL type, the PCR products obtained using an extracted plasmid (pECDF16) of one E. coli isolate (S79-1) as a template were sent for sequencing and the results revealed presence of blaC-
TX-M, blaTEM-1 and blaSHV-8 as deposited in the GenBank. It is worth noting that many studies had reported on abundance of blaTEM-1 among various members of Enterobacteriaceae. It is more likely that blaTEM-1 will not express ESBL phenotype unless amino acids substitutions takes place at certain posi-tions such as 104, 164, 238 and 240 [32, 33]. However, the presence of other ESBL genes such as blaSHV-8 and blaCTX-M on the same plasmid could be the main reason for expres-sion of ESBL phenotype. Moreover, our results revealed that this plasmid also codes for quinolones resistance, this was confirmed by successful recovery of transformed plasmid on Luria Bertani media with ciprofloxacin at final concentration 50μg/ml. Therefore, results obtained from this study are of a great clinical and environmental importance about horizontal transfer of ESBLs genes among population of clinically rel-evant Gram negative pathogens. Therefore, new guidelines should be undertaken in Egypt to regulate use of antimicro-bial agents and hence control transfer of microbial resistance among clinically relevant pathogens.
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